Image forming devices including copiers, laser printers, facsimile machines, and the like, include a drum having a rigid cylindrical surface that is coated along a defined length of its outer surface with a photoconductive material. The surface of the drum is charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the photoconductive surface exposed to light are discharged thus forming a latent electrostatic image on the photoconductive surface. A developer material, such as toner, having an electrical charge such that the toner is attracted to the photoconductive surface is brought into contact with the photoconductive surface. The drum then rotates past an intermediate transfer medium where the toner is transferred onto the medium. A recording sheet, such as a blank sheet of paper, is then brought into contact with the intermediate transfer medium and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated thereby permanently fusing the toner to it. In preparation for the next image forming cycle, the photoconductive surface is discharged and residual toner is removed.
The toner is stored in a toner reservoir adjacent to the drum. A doctor blade and developer roller are positioned between the toner reservoir and drum for controlling the amount of toner passed to the drum. A point created between the doctor blade and the developer roller controls the amount of toner transferred to the drum. It is important that the doctor blade make uniform and consistent contact across the entire length of the developer roller. If the doctor blade has inconsistent pressure with the developer roller during the transfer, uneven toner amounts will be transferred to the drum resulting in inconsistent and unacceptable print quality. If too much toner is transferred to the drum, printing errors may occur such as blurred images, poor color, and toner particles deposited on the background areas. Conversely, if not enough toner is transferred to the drum, the images will be too light and difficult to see.
A problem in maintaining consistent contact and pressure is the developer roller profile may be non-uniform requiring that the doctor blade move inward and outward to track the surface of the developer roller. Additionally, it is vital that contact be maintained across the entire length of the doctor blade to ensure even print quality across the width of the image.
One problem in prior systems is jitter caused by vibrations and velocity fluctuations in the developer roller during the printing process. Jitter shows up on a printed page as a repeating pattern of light and dark lines in the process direction that extend across the printed image. One cause of jitter is the doctor blade sticking to and slipping across the surface of the developer roller. The stick/slip movement causes the doctor blade to move back and forth which results in small perturbations on the developer roller which translate into small velocity variations.
One proposed solution is to lessen the amount of force that the doctor blade exerts on the developer roller. However, the amount of force applied by the doctor blade controls the amount of toner transferred to the developer roller. If the force is decreased to prevent or decrease jitter, toner transfer may be adversely affected. Also, it has been determined that lesser biasing force may prevent the doctor blade from sticking and skipping along the developer roller, but may not prevent vibrations that result in jitter. Further, another cause of jitter may be the electrical force between the developer roller and the drum. Lessening the amount of biasing force does not substantially reduce or eliminate this cause of jitter.
The present invention includes an apparatus and method of dampening a doctor blade within an image forming apparatus. In one embodiment, the apparatus includes a developer housing having an area for housing the doctor blade, a biasing member to bias the doctor blade against a developer roller, a member connected to a developer housing on a first side of the doctor blade, an extension connected to the developer housing and positioned on a second side of the doctor blade opposite the member on the first side, and a dampener attached to the extension and positioned between the extension and the doctor blade. In this embodiment, the dampener is constructed of a resilient material to dampen the movement of the doctor blade.
In another embodiment, the apparatus includes a developer housing having a first edge and a second edge positioned a distance apart for positioning a doctor blade, and a support extending between the first edge and the second edge. A first extension and a second extension each extend from the support and are equally distanced from a centerline of the developer housing.
In another embodiment, the apparatus is incorporated within an image forming apparatus which includes a developer roller, a doctor blade having a top edge and a bottom edge that contacts the developer roller, a biasing member that contacts the top edge of the doctor blade and biases the doctor blade against the developer roller, members positioned to contact a front side of the doctor blade, extensions positioned on a back side of the doctor blade, and dampeners positioned on the first extension. In this embodiment, the front side of the doctor blade contacts the members and the back side of the doctor blade contacts the dampeners.
The invention further includes a method of dampening a doctor blade by placing a dampening material against the doctor blade to dampen movement caused by sticking and slipping of a bottom edge of the doctor blade against the surface of a developer roller.